Mercury vapor discharge lamps have been used to generate UV radiation for initiating the curing of UV curable substances such as inks, furniture coatings, patterning of lithography resists, adhesives and three-dimensional modeling materials. However, mercury lamps are inefficient in their use of energy, take time to heat up and cool down and if broken can release mercury which is highly toxic. Accordingly, there is a move away from mercury discharge lamps and toward solid state UV radiation sources such as UV light emitting diodes (LEDs). UV LEDs can be rapidly switched on and off, are more energy efficient than mercury lamps and are safer to use. They are also more compact and can be less expensive than mercury lamps. The UV LEDs are generally used in the form of an array comprising a large number of individual LED chips. Some applications include an array UV LEDs that is a mixed array comprising LEDs having differing peak wavelengths in the UV region, thereby providing UV radiation having more than one peak wavelength.
The word “array” as used herein refers broadly to any collection of solid state radiation sources. The solid state radiation sources may be light emitting diodes, laser diodes, vertical cavity surface emitting lasers, polymer light emitting diodes (LEDs), electroluminescent devices, and any other suitable device which generates electromagnetic radiation via the recombination of holes and electrons. The array may comprise a mixture of different categories of solid state radiation source.
An array may include a collection of individual LEDs arranged, for example, in a rectangular pattern. The array may comprise a dense array of LED chips on a common substrate. For example, the array may include more than 10, optionally more than 50 solid state UV radiation sources. The array may comprise LEDs with specific wavelength, for example: 365 nm (I_line), 436 nm (G_line), 405 nm (H_line) or at least two types of solid state UV radiation sources having different peak wavelengths such that the UV radiation emitted by the module has more than one peak wavelength.